DBD::File / DBI::DBD::SqlEngine updates and doc review

Hi all,

as I didn't catch anyone on IRC, I remember that many of you
had questions about Pure-Perl device drivers basing on DBD::File
(or DBI::DBD::SqlEngine) for several reasons.

Currently we're finished most of development cycles for upcoming
DBI release and reworking the documentation. It might be a good
idea for anyone to read the updated documents from the sqlengine
branch or next dev-release.

We will try to answer all remaining questions about DBI driver
development (read: everything which isn't documented) with the
current doc update. Everything which is not clear, should be
asked.

Thanks in advance and merry Christmas for everyone.
-- 
Jens Rehsack